Apparatus for the treatment of biological tissue and corporal concretions

ABSTRACT

Disclosed is an apparatus for the treatment of biological tissue as well as for destroying concretions by means of focussed acoustic waves, having 
     a sound generating unit which a control unit triggers in such a manner that the unit generates acoustic waves of a specific frequency and energy, and 
     a focussing unit which focusses the generated waves in a focal area. 
     The present invention is distinguished by the sound generating unit (2) being provided, in an as such known manner, with a plane or only slightly curved radiation area in such a manner that the generated wave is an essentially plane wave and that the focussing unit (5) disposed in a fixed spatial relationship to the sound generating unit being provided with a Fresnel lenslike structure on the sound entry and/or sound exit area.

This application is a 371 of PCT/EP 94/01784 Jun. 1, 1994.

TECHNICAL FIELD

The present invention relates to an apparatus for the treatment ofbiological tissue and corporal concretions using focussed acoustic wavesaccording to the introductory part of claim 1.

STATE OF THE ART

In the course of the development of noninvasive therapeutic methods,procedures have been developed that generate a locally confined,controlled effect inside the body obviating traumatic penetration of thebody. One example of this is extracorporally induced lithotripsy inwhich short pressure pulses of high amplitude, which are focussed on theto-be-destroyed concretion, by way of illustration a kidney stone, aregenerated outside the body. When the energy density is high enough atthe site of the concretion, the concretion is crushed. An example ofsuch an apparatus is described in DE 38 35 318 C1, to which, in additionto the literature cited therein, reference is explicitly made withregard to all the terms not explained in more detail herein.Furthermore, it has been proposed to utilize energy concentrated withthe aid of highly energetic ultrasound waves for hyperthermy or forthermotherapy.

In all the processes in which focussed acoustic waves are employed forachieving successful therapy, it is necessary that the energy generatedoutside the body is coupled in exploiting suited "body windows" in thebody and steered to the predetermined target area by means of suitedlocating procedures. It must be taken into account that many organscannot be reached directly via suited "body windows". But rather theavailable body windows are of irregular shape, such as by way ofillustration the window through which ultrasound can be coupled into theliver or the urinary bladder. Moreover, it is often necessary to beam inthe ultrasound with a "slanted" respectively inclined direction ofincidence.

The hitherto proposed sound generating units such as, by way ofillustration, mentioned in DE 38 35 318 C1, i.e., by way of illustrationspherical caps, concave ellipsoids or paraboloids of rotation cantherefore only be employed in a restricted manner, because the circularshaped radiating areas of these sound generating units are not optimumlyadapted to the body windows at disposal. Moreover, if the coupling-indirection is slanted, the coupling media can only be poorly adapted tothe contours of the body.

As a consequence, only a part of the ultrasound generated outside thebody is at disposal for therapeutical purposes at the target site. Inaddition, regional and temporal focussing is frequently insufficient dueto phase disturbances on the propagation path (coupling medium andcorporal tissue). Furthermore, only a certain part of the generatedultrasonic energy is released into the coupling medium, because theacoustic impedances (density ρ * propagation velocity c) of the soundgenerator and of the tissuelike transmission respectively couplingmedium (often water) are very different especially when piezo-electricexciters are used so that the energy can only be partially coupled in.

The object of the present invention is to provide an apparatus for thetreatment of biological tissue using focussed acoustic waves, thisapparatus being easy to adapt to the different instances of applicationand not being restricted to circular radiation areas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a shows the fundamental concept of the present invention.

FIG. 1b shows an alternative embodiment using multiple adapting layers.

FIG. 2 shows the inventive transducer combined with a target locatordevice.

FIG. 3 shows use of the applicator on a patient.

FIGS. 4a, 4b, 4c and 4d show applicators of non-circular outline andtheir relationship to a target locator.

FIG. 5 shows wavelength relationship to various focal depth zones withinthe body.

An element of the present invention is that the sound generating unit isprovided with, in an as such known manner, a plane or only minimallyconcave or convex curved radiation area so that the generated wave isessentially a plane wave. In order to focus this essentially plane wave,the focussing unit disposed in a fixed spatial relationship to the soundgenerating unit has a Fresnel lenslike structure on its sound entryand/or sound exit area, Fresnel lenses are not only already known fromlight optics, but have also already been proposed for ultrasonic imagingsystems, by way of illustration in DE 29 19 176 C 2. Fresnel lenses ofthis type are designed in such a manner that coherent ultrasound at theindividual segments of the lens has a phase difference of n * λ (n=0,1,2. . . ) so that the ultrasound waves propagating through the adjacentzones of the lens interfere constructively in the focal zone whenleaving the lens.

The fundamental concept of the present invention is explained usingFIG. 1. A suited piezoelectric material 2 (e.g., Ba-titanate) is inclose contact with an adaption layer 1 (e.g. brass or the like)selectively with a similar impedance as the piezoelectric material orwith a quite different impedance (e.g., air in order to prevent energyradiation to the rear) and is connected toward the front toward theapplication side to a Fresnel lens 5 like the one described above or inpatent DE 29 19 176. Advantageous is the use of a lens material with animpedance lying between that of the piezoelectric ceramics and that ofthe connection medium. Possible materials are, e.g., aluminium or evenpolystyrene. Advantageous is also the use of one of the multipleadapting layers 3,4 which permit low-reflection impedance adaption ofthe generating material (e.g., piezo ceramics) to the coupling medium(e.g., water) and finally to the corporal tissue. The Fresnel lensitself can serve as the support structure of the entire compoundtransducer, resulting in little overall weight and easy handling. AsFIG. 2 shows, such a Fresnel compound transducer can be combined with asuited locating device 8 for representation and control of the targetarea 10 as well as with a variable control distance 6 for adaption tovarying anatomical conditions.

The use of suited coupling media 6 (e.g., water, US coupling gel, geldisks, or the like) permits adapting the anatomically given spacebetween the applicators and the surface of the body. Coupling medium 6can, e.g., be confined by a flexible cushion 7.

FIG. 3 shows a possible use of such an applicator on a patient.

Due to its flat design, the applicator can be easily placed on thepatient's body. The diagnostic ultrasound permits locating the targetarea: handling is similar to that of a diagnostic ultrasonic -B-imagetransducer on a patient.

Depending on the anatomical conditions, apart from applicators ofcircular outline, applicators of any desired shape can also be realizedand the position as well as the orientation of the locating componentcan be varied. Some examples are shown in FIGS. 4a, 4b, 4c and 4d Thearrangement shown in FIG. 4c is suited, e.g., for treating anomalies ofthe prostate gland through the filled urinary bladder with a downwardoffset beam direction. Other suited applicators which are adapted to thespecial windows and beam directions can be fixed in almost any desiredmanner. For instance, energy input can be optimized and adapted to thespecial anatomical conditions without being tied to the usually circularcoupling window predetermined by the device.

Another advantage of the present invention is that when utilizing awideband transducer the focal distance from the applicator can bechanged by varying the excitation frequency. Thus, by raising theultrasound frequency, the focus can be generated closer to theapplicator and by lowering the frequency, it can be shifted fartheraway.

This "zoom effect" permits treatment without a variable controldistance, resulting in advantages with regard to loss-free coupling andlow phase disturbances. Improved energy concentration results inimproved localized and more effective focal and therapy zones.

As shown in FIG. 5, various depths in the body zones can be reached fromthe surface of the body in direct contact of the applicator to the skin.

What is claimed is:
 1. An apparatus for the treatment of the human bodyby means of focussed acoustical waves, comprising:a sound generatingunit shaped so that its generated wave is an essentially plane wave, andhaving an acoustical impedance, said sound generating unit beingtriggered by a control unit to generate acoustic waves having a selectedspecific frequencies and energies; a rigid focussing unit comprising aFresnel lens-like structure disposed in a fixed spatial relationship tosaid sound generating unit whereby said focussing unit focusses thewaves generated by said sound generating unit in a desired selectedfocal range, the material of said focussing unit having an acousticalimpedance; manipulation means attached to said focussing unit forpositioning said apparatus relative to a human body; a coupling mediumfor coupling said focussing unit to a human body said coupling mediumhaving an acoustical impedance; the acoustical impedance of saidfocussing material lying between the acoustical impedance of said soundgenerating unit and the acoustical impedance of the coupling medium,said coupling medium being situated in the sound path between saidfocussing unit and said human body, said focussing unit serving as acarrier for the entire structure; and at least one adaption layerpositioned between said radiation area of said sound generating unit andof said sound entry area of the focussing unit, the acoustical impedanceof said adaption laying between that of said focussing unit and that ofthe acoustical impedance of said sound generating unit.
 2. An apparatusaccording to claim 1, in which said focussing unit is connected directlyto its sound entry area or via at least one adaption layer to theradiation area of said sound generating unit and having with a Fresnellenslike structure on its sound exit area.
 3. An apparatus according toclaim 2 in which adaption layer is provided between said radiation areaof said sound generating unit and the sound entry surface of saidfocussing unit having an impedance which lies between that of saidfocussing unit and the impedance of said sound generating unit.
 4. Anapparatus according to claim 3, in which said adaption layer islow-reflecting.
 5. An apparatus according claim 3, in which saidadaption layer is at least partially λ/4 layers.
 6. An apparatusaccording to claim 1 in which said focussing unit is composed of amaterial the acoustic impedance of which lies between the impedance ofsaid sound generating unit and the impedance of the medium which issituated in the sound path behind said focussing unit.
 7. An apparatusaccording to claim 1, in which at least one said adaption layer is beingdisposed on the interface of said sound generating unit opposite saidradiation area.
 8. An apparatus according to claim 7, in which saidadaption layer disposed on said opposite interface having either asimilar impedance to the one of said sound generating unit or having avery different one.
 9. An apparatus according to claim 1 in which saidsound generating unit is provided with a piezotransducer.
 10. Anapparatus according to claim 1, in which said focussing unit serves asthe carrier body for the entire structure.
 11. An apparatus according toclaim 1, in which said sound generating unit is provided with a multipleof individual transducers.
 12. An apparatus according to claim 11, inwhich said individual transducers are arranged mosaic-like.
 13. Anapparatus according to claim 11, in which said individual transducershave the shape of concentrically disposed rings.
 14. An apparatusaccording to claim 13, in which said rings being constructed likeFresnel zones.
 15. An apparatus according to claim 11 in which saidcontrol unit triggers said individual transducers separately.
 16. Anapparatus according to claim 15, in which said control unit triggerssaid individual transducers with varying phase positions.
 17. Anapparatus according to claim 15 in which said control unit triggers saidindividual transducers each with a different frequency.
 18. An apparatusaccording to claim 1, in which a locating device is provided permittinglocating a to-be-treated region.
 19. An apparatus according to claim 18,in which said locating device is disposed in the central region of saidsound exit area of said focussing unit.
 20. An apparatus according toclaim 18, in which said locating device is disposed outside said centralregion of said sound exit area of said focussing unit.
 21. An apparatusaccording to claim 18 in which said locating device is provided with anX-ray locating device.
 22. An apparatus according to claim 18, in whichsaid locating device is provided with an ultrasonic locating device. 23.An apparatus according to claim 22, in which said ultrasonic locatingdevice is an ultrasonic B-imaging device.
 24. An apparatus according toclaim 1 in which said sound exit area of said Fresnel lens-likestructure having a rotationally symmetrical shape.
 25. An apparatusaccording to claim 1 in which said sound exit area of said Fresnellenslike structure is a shape adapted to the respective treatment case.26. An apparatus according to claim 1, in which said control unit variesthe frequency with which it triggers said sound generating unit in orderto vary the focal position.
 27. An apparatus according to claim 1 inwhich a coupling medium is provided between said sound exit area of saidfocussing unit and the coupling region of the to-be-treated body.
 28. Anapparatus according to claim 27, in which said coupling medium isconfined by a flexible cushion.
 29. An apparatus according to claim 27in which said coupling medium forms a variable control distance.